timbosan:I don't get how this solution meets the OP's request for "as good as factory fitted" - you have to manually change inputs on the stereo, you have to ensure the stereo actually has a 3.5 inch phono input, it cannot (by design) sync phonebooks, etc. Also its not a very stealth install when its stuck on the front of the dash with a cable hanging down!
I bought two of these a year or so ago and now also have a car fitted with a Dension unit. Even though the Dension cost hundreds, is supposedly 'factory fit' and sync's the phonebook etc I would take the Kinivo units all day long.
They connect first time, every time to whoever gets in the car as they connect to both mine and my wifes phones. Call quality is superb and using bluetooth for the radio and music is great.
To answer your questions though. If, like me, you use your phone for radio and music you never need to switch from Aux. Of course you need to know your car has Aux-in in the first place but it is pretty standard these days and it's not all that hard to do if you dont have it. Either buy a replecement headdeck or make an aux-in to replace the cd changer. I did it for my E39 BMW in about 20 minutes for less than $2.
Finally hiding them from view is so easy it's funny. Both of mine are in ashtrays meaning they are both easily accesible if I want to use the USB charging and both removed from view. If you want to spend hundreds of dollars then do so.
But a little research and a little effort means I have a brilliant, steathly solution for not much more than the $60 they cost.